Mismatched type for fortio response

*Title*: *Mismatched type for fortio response causes failure in interconversion*

*Description*:
The message format in protobuff here https://github.com/envoyproxy/nighthawk/blob/f42add9bb5c71a5652db2f9471dda357b96d5ee2/api/client/transform/fortio.proto#L31 mismatches the expected datatype by fortio here https://github.com/fortio/fortio/blob/d2a2d42f4f17df4c09e608353546ebd0d443747d/periodic/periodic.go#L221 on the field `RequestedQPS`

This is causing Unmarshalling to fail while conversion from one to another.
*Reproduction steps*:
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*Call Stack*:
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